Bi-directionally releasable circuit breaker



April 1960 w. H. MIDDENDORF. 2,934,624

BL-DIRECTIONALLY RELEASABLE CIRCUIT BREAKER Filed Feb. 25, 1957 2 Sheets-Sheet 1 INVFNTOR. a: MW

n'rmeueys. A

April 26, 1960 w. H. MIDDENDORF 2,934,624

BI-DIRECTIONALLY RELEASABLE CIRCUIT BREAKER Filed Feb. 25, 1957 2 Sheets-Sheet 2 INVENTOR.

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United States Patent BI-DIRECTIONALLY RELEASABLE cmcurr BREAKER it William H. Middendorf, Covington, Ky., assignor to The Wadsworth Electric Manufacturing Company, Inc., Covmgton, Ky., a corporation of Kentucky Application February 25, 1957, Serial No. 642,035

12 Claims. (Cl. 20011'6) This invention relates to electric circuit breakers and is directed particularly to paired circuit breakers, each releasable in consequence of circuit overload, and a trip device which is common to the circuit breakers for mechanically eifecting the release of one when the other is tripped by overload.

The common electric circuit breaker used in distribution circuits or the like is an automatically operable switch adapted to open a circuit in the event the circuit becomes overloaded, thereby terminating the fire hazard which would otherwise result from over-heating of the circuit wires. In some instances, it is desirable or necessary for safety reasons to install independently operable circuit'breakers in each of the legs of a circuit so that each leg will be protected individually. For this purpose,

the legs of a circuit, but each will operate independently of the other, Whereas it is desirable or necessary for both circuit legs to be opened when either becomes overloaded.

A principal objective of this invention has been to provide circuit breakers which are individually adapted for single circuit service but which are equally adapted, by attachment of a common trip element, for service in pairs as a multi-pole circuit breaker wherein each'circuit breaker, when tripped through electrical overload, will mechanically effect the tripping of the other circuit breaker of the pair and thereby open both legs of a multi-pole circuit when either leg becomes overloaded.

A further objective of this invention has been to provide a multi-pole unit comprising single circuit breakers which are individually the same as one another but which are adapted for multi-pole cooperation by means of a simple common trip element such that the economy of mass production of single circuits units may be realized and such that multi-pole circuit breakers readily may be provided when necessary by assembly of the single circuit units with the simple common trip device.

Another objective of this invention has been to provide a single circuit breaker comprising cooperable latch elements which are normally engaged when the circuit breaker is in a closed position and disengaged when the circuit breaker is in open circuit condition, in conjunc- Nice tive to circuit load conditions, or both, and separate means for efiecting disengagement of the latch elements without moving or bending any or all of such elements from the positions they occupy when the circuit breaker is closed. In this regard, for example, the invention contemplates a circuit breaker which is releasable under circuit overload by warping movement of a calibrated bimetal member and which is independently releasable regardless of the load condition of the circuit to which that breaker is con: nected without moving the bimetal element in any direc tion. I By this provision, the bimetal element is caused to move only when circuit overload requires tripping of the breaker but is otherwise protected against movement which might otherwise cause it to become permanently bent or warped and thereby cause the circuit breaker to become desensitized or decalibrated.

Another objective of the invention has been to provide a circuit breaker having a stationary contact, a carrier having a contact cooperable with the stationary contact 'and movable through one path to effect engagement and disengagement of the stationary and movable contacts, a

tion with means for moving one of the latch elements I pendently of circuit conditions prevailing in the circuit breaker.

A still furtherobjective of this invention has been to provide a circuit breaker having cooperable latch elements, one of which is carried or controlled by one or more elements responsive thermally or magnetically sensicurrent-responsive releasable latch for normally holding the carrier in position in which the contacts are engaged, and means for efiecting disengagement of the latch by movement of the carrier in a different path or direction to mechanically effect the tripping of the circuit breaker. The present invention particularly contemplates means for moving the carrier in a second direction in the form of a trip element which is responsive to the tripping movement of the second breaker of a pair.

Other objectives and further features of the present invention-appear in the following detailed description of the drawings in which a typical embodiment of the invention is disclosed.

In the drawings:

Figure 1 is a sectional elevation of a circuit breaker constructed in accordance with this invention with the parts shown in the circuit-closed position;

Figure 2 is a somewhat diagrammatic view similar to Figure l'but showing the parts in the circuit-open position;

Figure 3 is a cross-sectional view through a pair of single pole circuit breakers equipped for multi-pole service in accordance with the present invention, as taken on the line 33 of Figure 1;

Figure 4 is a fragmentary cross-sectional view taken on the line 44 of Figure 1;

Figures 5, 6, and 7 are diagrammatic views showing the operation of a trip element which is common to a pair of circuit breakers in accordance with this invention; in which Figure 5 shows the movement of the common trip element at the moment when one of the circuit breakers becomes tripped in response to overload; Figure 6 shows the movement and eifect of the common trip element when the other of the circuit breakers becomes tripped in response to overload independently of the first; and Figure 7 shows the position of the common trip element and the latching movements which occur upon resetting of the circuit breaker; and

Figure 8 is a sectional view similar to Figure 4 but showing a modified form of mounting to accommodate mechanical unlatching.

Although the tripping mechanism of the present invention is simple in nature and may be produced at very low cost, an understanding of the mechanism with which it cooperates is desirable in order to understand the manner in which it functions; therefore, the main operating mechanism of the circuit breaker shown in the drawings is first described, although the manner in which the main operating parts function generally does not form a part of the present invention. 1

The single pole circuit breaker selected to illustrate an turn, is pivotally movable about the axis of a cross shaft 7 having its ends supported in the casing 2. Adjacent a side wall of the casing, and to one side of the carrier 6, a lever 9 is pivotally mounted to the casing wall, as at 10. The upper end of lever 9 is bent over the carrier 6, as at 11, to provide a hook 12 to which one end of a tension spring 13 is attached. The opposite end of the tension spring is connected to arm 4, which may be slotted suitably to clear the spring. The upper end of lever 9 is straddled by a handle 14 which is reciprocably mounted at the top of the casing 2. Spring 13 biases the rocker rotationally about the axis of shaft 7, and the rocker is movable (in counter-clockwise direction as seen in Figure 1) independently of the lever 9, but the rocker has a shoulder 15 which is engageable by the lever to efiect return movement of the rocker in the opposite direction.

Rocker 6 is of bifurcated construction and one of its side arms 17, i.e. the one adjacent lever 9 in the structure shown, is bent over as at 18 to form a latching element. This element cooperates with a latching member 19 which projects from a thermally-responsive member or bimetal 28 having its lower end in electrical connection with a circuit terminal 21 through an electrically conductive strap 22 on which the bimetal is supported and to which it is electrically connected as at 23. A flexible electrical conductor or so-called pigtail 25 extends from the upper portion of the bimetal 20 into electrical connection with arm 4, whereby a conductive path is furnished through the arm 4 to the movable contact 3. Stationary contact 1 is mounted on an electrically conductive strap 26 which, in the construction shown though not necessarily, terminates in a jaw 27 adapted for sliding, frictional interconnection with a conductive prong extending from a bus bar or the like (not shown). The circuit breaker is installed in the circuit or circuit leg which is to be protected by connection across jaw 27 and terminal 21.

Since bimetal 20 is in the circuit which is completed through contacts 1 and 3 when they are engaged, the bimetal is thermally responsive to the current magnitude. When heated, as when an overload occurs, the bimetal warps or bends, thereby causing latch member 19 which is associated therewith to move in the direction for unlatching, that is, to the right as shown in Figure 1. If the overload is of sufiicient magnitude, bimetal 20 will move sufficiently for the latching member 19 to clear the latching member 18 associated with the carrier 6. Since spring 13 is tensionally connected toarm 4, the arm 4 bearing against the crotch in the carrier causes the carrier 6 to rotate about the axis of shaft 7 and as the carrier rotates, the upper end of the arm 4 follows the crotch. The arm 4 thereby swings to the open circuit position in which it is shown in Figure 2. In this position it will be noted that the point of connection of spring 13 to arm 4 has moved to an over-center position with respect to the point of engagement of the arm with the carrier, and' the spring 13, therefore, biases the arm 4 to the open position wherein rests against stop 30 provided on the casing 2.

By moving the handle 14 to the right from the position in which it is shown in Figure 1, the lever 9 is caused to bear against stop 15 provided on the rocker and thereby rotate the rocker about the axis of shaft 7 in a clockwise direction (with respect to Figure 2), thereby lowering the latch element 18 to a position where it is re-engageable with latch member 19. Assuming that bimetal 20 has cooled sufiiciently to move from the warped condition in which it is shown in Figure 2 to the relatively unwarped condition in which it is shown in Figure 1, the latch member 19 will thereby have been returned to a position where it is re-engageable by latch member 18. This reengagement may be facilitated by chamfering the approach edge of latch member 19 whereby it will be carnmed away to permit the latch member 18 to pass beneath its lower surface.

During this movement the spring 13 continues to bias arm 4 against the rocker but, since the force line to the rocker remains on the same side of the pivot point of the arm as that in which it is shown in Figure 2, the arm 4 will remain in the open circuit position after latching of the rocker. However, after the handle 14 has been shifted to the right to effect the relatching, it is then shifted to the left, and as it is returned to the position in which it is shown in Figure l, the line of force provided by the spring will move relatively to the other side of the pivot point of arm 4, and the spring will thereby swing arm 4 so as to carry contact 3 into engagement with contact 1.

If it is desired to provide means for releasing the rocker magnetically as well as thermally, in order to trip the circuit breaker in event of instantaneous high overload, the bimetal may be equipped with a magnetic yoke 34 which is mechanically cooperable with an armature 35 arranged to effect movement of the bimetal through magnetic attraction and thereby cause displacement of latch member 19 to unlatching position. The armature 35 may either be mounted stationarily in the case, in normally spaced relation to the armature 35, or other suitable construction may be employed. In the drawing a magnetic release device is shown which conforms to the disclosure of Middendorf US. Patent 2,716,679, dated August 30, 1955.

As much of the circuit breaker as has been described up to this point does not form the substance of the pres ent invention, and it will be understood that other types of operating mechanisms may be employed in utilization of the principles which are hereinafter discussed. Also, it will be understood that the case within which the operating parts are housed may be of any suitable form other than the one disclosed. In the drawing the case illustrated comprises hollow half case sections 38 and 39 which mate with one another at the meeting face 40 to provide a cavity 41 defined by spaced side walls 42 and 43 between which the operating parts of the main circuit breaker mechanism are housed. A pair of sin gle pole circuit breakers intended to constitute a multipole circuit breaker may be paired together by suitable cross bolts or rivets 44, and the handles of a pair of circuit breakers may be tied together for movement in unison in the usual manner.

In accordance with the present invention, a trip member 45 is provided which is movably responsive to each of the rockers of a pair of single pole circuit breakers and which is effective, in consequence of movement incidental to the release of either rocker, to cause disengagement of latch member 18 from latch member 19 of the other circuit breaker by moving the same in a sidewise direction, that is, a direction generally lateral to the plane or path of movement through which latch member 19 moves in causing disengagement under electrical overload.

To accommodate such movement, the rocker of each circuit breaker, or at least the latch portion 18 thereof, is resiliently movable in sidewise direction. Thus, for unlatching under electrical overload, the latch member 19 of each circuit breaker moves away from latch member 18 sufiiciently to cause disengagement of the two, and for unlatching of either circuit breaker mechanically in consequence of the release of an adjacent circuit breaker of a multi-pole pair, latch member 18 moves away from latch member 19 in a direction sidewise or lateral with respect to the aforesaid normal path of movement of latch member 19. To provide for sidewise movement of latch member 18, in the construction shown the entirerocker of each circuit breaker is shiftable sidewisely. For this purpose, the bore 47 through which each rocker pivotally engages cross shaft 7 is slightly larger than the diameter of the cross shaft 7, as shown in Figure 1, whereby the rocker is movable angularly with respect to the axis of the cross shaft sufiiciently to permit latch member 18 of the rockers to clear the side edge of the electrically responsive latch member 19. However, each rocker is biased against sidewise movement or angulation by a. compression spring 43. The spring respectively surrounds shaft 7 and one end of the spring is seated in a recess of the case while the other end of each spring bears against a side wall of the rocker, 'as is shown in Figure 4.

Cross strap 45 straddles the rockers and extends from one circuit breaker to the other through apertures provided in the side Walls of the circuit breaker. The cross strap may be in the form of an electrically insulative stamping made of high rag content fiberboard or the like. Interconnection of the cross strap with the rockers of the circuit breakers is provided by bores 50, 5%) through which extend the portions of the respective rockers adjacent latch members 18 thereof. These bores are somewhat larger than the rocker portions received thereby, for reasons subsequently explained. In addition, cross strap 45 comprises fulcrum portions 52 and 53 which bear respectively upon the corresponding side walls of the circuit breakers but at points 54 and 55 located respectively above and below the points of interconnection of the cross strap with the rockers.

Description of operation When the circuit breakers of a multi-pole pair are both latched, the cross strap 45 is in the position in which it is shown in Figure 3. Let it now be assumed that an overload condition occurs in the circuit leg which is served by the right-hand circuit breaker shown in Figure 3 and that it is desirable or requisite that the circuit breaker on the left, serving the other leg, be tripped. When the right-hand circuit breaker is released, the rocker thereof rotates about the axis of shaft 7 carrying the right-hand end of the common trip element 45 upwardly with it. Since the left-hand circuit breaker at this moment remains untripped, the common trip element moves pivotally about the point to which it is connected to the rocker in the left-hand circuit breaker, but the fulcrum portion 52 within the left-hand circuit breaker bears against the wall of that circuit breaker, as at point 54 (Figure 5). Since the wall is immovable, and since the rocker of the right-hand breaker is now moving at relatively high speed under the infiuence of the tension spring 13, the point of engagement of the common trip 45 with the rocker in the left-hand circuit breaker moves arcuately to the right. However, it will be noted that the bore through which the common trip engages the rocker in each circuit breaker is sufficiently large to provide clearance, because of which the portion of the rocker within the bore slips vertically to eliminate the upward thrust upon latch member 19 which would otherwise be imposed thereon through the vertical component of the arcuate movement. In other words, only the sidewise force component is utilized, and the upward component of arcuate movement is absorbed by slippage of the rocker in the cross strap bore. Thus, the upward movement of the right-hand side of the cross strap exerts a sidewise unlatching movement of the rocker of the lefthand circuit breaker and it trips virtually simultaneously with the tripping of the right-hand circuit breaker.

A similar release is effected when the left-hand circuit breaker trips under electrical overload while the right-hand breaker remains latched. -This condition is illustrated in Figure 6. In this instance, fulcrumportion 53 of the common trip member 45, bearing upon the case wall of the right-hand circuit breaker below the point of engagement of the cross strap with a rocker thereof, acts as a fulcrum to shift the latch member 18 of the right-hand breaker to the right as the left end of the cross strap is carried upwardly inconsequence to electrical overload release of the rocker of the left-hand breaker. Here, again, the cross strap moves arcuately about the point of engagement with the rocker, i.e., about fulcrum point 55, out here again, the vertical component of the arcuate movement is accommodated as slippage of the rocker within the encircling bore of the cross strap, and the latch member of the left-hand latch member therefore moves only sidewisely. T

As a matter of manufacturing convenience, the portions of the rockers encircled by the bores of the cross strap 45 may be rectangular in cross section, conforming to the shape produced by common punching, but it will be understood that rounding of the corners in these crosssectional areas will facilitate vertical slippage if a greater effect is required than the one produced by the structure shown.

The rockers move or angulate sidewisely to unlatching positions against the biasing forces provided by the respective compression springs 48. However, as soon as the rockers are released from their latches, the compresion springs 48 restore the rockers to the position in which they are shown in Figure 4. For relatching, sidewise movement of the rockers is again desired to permit a downward movement of the latch members 18 past the latch members 19 without necessitating the bending of the bimetal. To facilitate such movement, the lower edges of the latches 18 or the upper edges of the latch members 19 may be rounded to exert a camming action through which the latch members 18 will be shifted sidewisely in passing the latch member 19, after which the compression springs 48 will cause the latch members 18 to assume positions beneath the latch members 19. In the construction shown, and particularly as illustrated in Figure 7, the lower edges of the cam members 18 are curved to present cam-like faces 56.

A modified construction for the rocker mounting is shown in Figure 8 wherein a type of universal joint is employed to support shaft 7. In this instance, the cross bore in each rocker is just large enough to receive shaft 7 and permit rocker rotation without looseness. Compression springs 48 urge the rockers sidewisely upon the shafts as previously described. However, each shaft '7', instead of being mounted in the side walls of the case, passes through a shank 57 of a pin which is rotatably supported in a cross Wall 58 of the case, beneath which 'the pin carries a head 59. The socket or recess within which spring 48 is sustained is slightly larger than the outer diameter of the spring, and therefore, it will be seen that sidewise movement of a latch end of the rocker is permitted through slight angular rotation of pin 57 which supports shaft 7 on which the rocker is carried. The parts are held in assembly through the upward pull upon the rocket afforded by spring 13.

The present invention may be utilized in conjunction with various other types of circuit breaker mechanisms other than the one shown, it being understood that circuit breakers commonly are available comprising cooperable latch members, one of which is movable to unlatching position in response to electrical overload. To incorporate the present invention in such structures, it is necessary only that the other of the latch members be arranged for movement in a direction lateral to the direction in which the first moves to an unlatching position, whereby such lateral movement readily may be caused to occur by means of a trip element of the type shown. While the fulcrum points of the trip plate shown in the drawings are located respectively above and below the points of engagement of the trip plate with the carriers of the circuit breakers, it will be undesrtood that the fulcrum points, if desired, may both be offset either above or below such points of connection to provide a similar type of operation. If located below thepoints of connection, the fulcruins at the ends of the strap may be 7 arranged to engage adjacent side walls of adjacent breakers, or if above, then the fulcrums may be arranged to engage the outside walls of adjacent breakers.

Having described my invention, I claim:

1. A multi-pole circuit breaker comprising a plurality of stationary contacts, contact carriers respectively serving the stationary contact and having surfaces thereon which are engageable therewith, means biasing each contact carrier for movement of the contact surface thereon away from the said stationary contact therewith, latch means individual to each carrier for releasably holding the same in a first position in which its contact surface engages the stationary contact served thereby, each carrier being bodily movable to a second position to release it from said latch means, current-responsive means individual to each carrier for releasing the same for movement of its said surface to a contact-disengaging position, a rotatively operable trip member in connection with all of said carriers said trip member being engageable with said carriers for bodily moving said carriers to said second position independently of the current-responsive means therefor, and means responsive to the movement or each carrier upon release thereof under current overload for imparting rotation to said rotatable trip member.

2. A pair of single pole circuit breakers each having eooperable contacts, a pair of releasasle latch means normally movable in a plane for holding the respective contacts in engagement and current-responsive means for releasing said releasable latch means, a cross strap having portions respectively fulcrumed on each circuit breaker and pivotally communicating with each circuit breaker of the pair, means for pivoting the strap in a plane transverse to the normal movement of said latch means about the respective fulcrum points thereof in consequence of the release of the respective adjoining circuit breaker, and means responsive to pivotal movement of the cross strap about such fulcrum point for releasing the other circuit reaker of the pair independently of the current-responsive releasable means.

3. Single pole circuit breakers in assembly for multipole service, each single pole circuit breaker comprising a stationary contact, a movable carrier having thereon a contact surface engageable with said stationary contact,

means for moving said carrier to a position in which said stationary contact and contact surface are disengaged, a current-responsive control device, releasable latch means controlled by said device, said releasable latch means comprising cooperable elements, the first movable to a latch-releasing position by said control device in response to electric overload, the second associated with said carrier and movable to a latch-releasing position upon movement of said carrier in a direction laterally away from said first latch element, a strap member having fulcrum engagement at each of its respective ends with said circuit breakers, a trip shaft common to all of the single pole breakers of the assembly, said shaft being bodily pivotable about its fulcrum ends and having connection with the carriers of said circuit breakers to effect movement of said carriers into said latch-releasing positions thereof upon bodily movement of said strap, and means for elfecting bodily movement of said strap in consequence of the movement of each carrier upon release thereof.

4. In combination, a pair of circuit breakers, each circuit breaker having cooperable contact members, a carrier for movably effecting their engagement and disengagement, means for moving the carrier to disengage the contacts, a latch normally engaging and holding the carrier in a positon in which the contacts are engaged, a current-responsive device for releasing said latch in event of overloading of a circuit completed through said contacts when they are in engagement, and means for moving said carrier to a position in which it is disengaged from said latch independently of said current-responsive means, comprising a plate having engagement with each 8 carrier and having fulcrums respectively engaging stationary parts of each circuit breaker about which fulcrums said plate is pivotal in consequence of release of either carrier for moving the other carrier to latch-disengaging position.

5. In a multi-pole circuit breaker comprising circuit breaker units each of the type comprising a stationary contact, a movable carrier having associated therewith a contact engageable and disengageable with the stationary contact in consequence of movement of the carrier to contact engaging and disengaging positions, means biasing the carrier to contact-disengaging position, a latch for holding the carrier in contact-engaging position, and a current-responsive control device, said latch compris ing cooperable elements, one movable to latch-releasing position by said current-responsive control device, the other movable to latch-releasing position by movement of said carrier in a direction generally lateral the direction in which the first of said elements moves to releasing position, the improvement which comprises a trip strap in connection with the carrier of each circuit breaker whereby the trip strap is shifted bodily in consequence of movement of the carrier of any circuit breaker under the influence of the biasing means therefor, and fulcrum means responsive to said bodily movement of said cross strap for moving the carrier of an adjacent circuit breaker to its latch-disengaging position through the connection of the trip strap therewith.

6. In combination with a pair of circuit breaker units each comprising cooperable contacts, a carrier pivotally movable for separating the contacts, means biasing the carrier toward movement in contact-separating direction, a latch comprising releasably cooperable elements for normally holding the carrier against pivotal movement, one of said elements being shiftable to an unlatching position by movement in a direction generally parallel to the plane through which said carrier is pivotally movable, the other of said latch elements being shiftable to an nnlatching position by movement in a direction lateral to the plane of movement of the carrier, current-responsive means for moving the first of said elements to its unlatching position in consequence to circuit overload, means for moving the other of the latch elements of each circuit breaker to its unlatching position, said means comprising a cross strap common to both circuit breakers of the pair movably associated with the carrier of each and operatively connected to the second of said latching elements of each circuit breaker unit whereby release of a carrier of either circuit breaker of the pair under circuit overload effects arcuate movement of said cross strap, and fulcrum means for translating the arcuate movement of the cross strap caused by release of the carrier of either one of said circuit breaker units into a thrust of the cross strap in a direction effective for shifting the second of said latch elements of the other of the circuit breaker units to unlatching position.

7. In combination with a pair of circuit breaker units comprising a walled case and, within said case, cooperable contacts, a carrier pivotally movable for separating the contacts, means biasing the carrier toward movement in contact-separating direction, a latch comprising releasably cooperable elements for normally holding the carrier against pivotal movement, one of said elements being shiftable to an unlatching position by movement in a direction generally parallel to the plane through which said carrier is pivotally movable, the other of said latch elements being shiftable to an unlatching position by movement in a direction lateral to the plane of movement of the carrier, current-responsive means for moving the first of said elements to its unlatching position in consequence to circuit overload, means for moving the other of the latch elements of each circuit breakerto its unlatching position, said means comprising a cross strap common to both circuit breakers of the pair movably associated with the carrier of each and operatively connected to the second of said latching elements of each circuit breaker unit whereby release of a carrier of either circuit breaker of the pair under circuit overload effects arcuate movement of said cross strap, and fulcrum means at the opposite endwise positions of said cross strap bearing respectively upon the said walls of said case for translating the arcuate movement of the cross strap caused by release of the carrier of either one of said circuit breaker units into a thrust of the cross strap in a direction effective for shifting the second of said latch elements of the other of the circuit breaker units to unlatching position.

8. in combination with a pair of circuit breaker units comprising a walled case and, within said case, cooperable contacts, a carrier pivotally movable for separating the contacts, means biasing the carrier toward movement in contact-separating direction, a latch comprising releasably cooperable elements for normally holding the carrier against pivotal movement, one of said elements being shiftable to an unlatching position by movement in a direction generally parallel to the plane through which said carrier is pivotally movable, the other of said latch elements being shiftable to an unlatching position by movement in a direction lateral to the plane of movement of the carrier, current-responsive means for moving the first of said elements to its unlatching position in consequence to circuit overload, means for moving the other of the latch elements of each circuit breaker to its unlatching position, said means comprising a cross strap common to both circuit breakers of the pair movably associated with the carrier of each and operatively connected to the second of said latching elements of each circuit breaker unit whereby release of a carrier of either circuit breaker of the pair under circuit overload effects arcuate movement of said cross strap, and fulcrum means at the opposite endwise positions" of said cross strap bearing respectively upon the said walls of said case for translating the arcuate movenTnt of the cross strap caused by release of the carrier of either one of said circuit breaker units into a thrust of the cross strap in a direction effective for shifting the second of said latch elements of the other of the circuit breaker units to unlatching position at points respectively offset with respect to the points at which said cross strap is operatively associated with the carriers within said case.

9. In combination with a pair of circuit breaker units each comprising cooperable contacts, a carrier movable to separate the contacts, means biasing the carrier toward movement in contact-separating directio'n, a latch comprising releasably cooperable elements for normally holding the carrier against movement in contact-separating direction, said elements each being movable to laterally related unlatching positions, current-responsive means for moving one of the elements to its unlatching position in consequence to circuit overload, and means for moving the other of the latch elements of each circuit breaker laterally to its unlatching position, said means comprising a trip device operatively responsive to the carriers of both circuit breaker units and operatively connected with the said other of the latching elements of each whereby release of a carrier of one circuit breaker of the pair under circuit overload effects lateral unlatching movement of the cooperable element of the carrier of the other circuit breaker of the pair independently of the circuit load therein.

10. A multi-pole circuit breaker comprising a pair of single circuit breaker units each of the type having a pair of cooperable contacts, a carrier for moving one of the contacts from the other, spring means for biasing said carrier toward movement in contact-separating direction, a latch comprising cooperable elements which are normally engaged for holding the carrier against movement under the influence of said spring means, a current-responsive device for moving a first of said elements to an unlatching position in a first direction a cross strap common to both of said circuit breaker units and having its respective endwise portions operatively connected to the second of said elements to effect movement of the second of said elements, and means responsive to unlatching of the carrier of either circuit breaker for moving said cross strap in a direction effective to move the second latching element in the other circuit breaker to unlatching position in a second direction lateral to said first direction.

11. A multi-pole circuit breaker comprising a pair of single circuit breaker units each of the type having a pair of cooperable contacts, a spring-biased carrier movable in a plane for moving one of the contacts from the other, a latch comprising cooperable elements normally engaged for holding the carrier against spring bias, current-responsive means for moving one of said latch elements, and means interconnecting the carriers of the respective circuit breakers, said interconnecting means being movable by movement of either one of said carriers in said plane, said interconnecting means, upon movement thereof by said one carrier, moving said other carrier and its cooperable latch element in a direction lateral to said plane of movement of said carrier to an unlatching position.

12. A multi-pole circuit breaker comprising a pair of single circuit breaker units each of the type having a pair of cooperable contacts, a member movable in a plane for separating the contacts one from another and also movable in a generally sidewise direction lateral to the said plane, spring means for biasing said member toward movement in contact-separating direction, spring means for biasing said member against generally sidewise movement, a latch comprising cooperable elements which are normally engaged for holding the member against movement under the influence of said first spring means, one of said elements being connected to said member and movable to an unlatching position upon sidewise movement of said member against the bias of said second spring means, a current-responsive device for moving the other of said elements to an unlatching position in consequence of circuit overload, a cross strap common to both of said circuit breaker units, said cross strap having its opposite endwise portions operatively connected to the respective members of the circuit breaker units of said pair whereby each endwise portion of said cross strap is movable with the member to which it is connected upon release of either of said members from said latch there for, means providing a sidewise mo'tion to said strap in consequence of movement of either endwise portion thereof, and means for exerting the sidewise motion of the strap effected by the unlatching of said member of one circuit breaker unit upon the said member of the other circuit breaker unit to effect unlatching of the latter.

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